An innovative concept of use of redox-active electrolyte in asymmetric capacitor based on MWCNTs/MnO 2 and Fe 2 O 3 thin films.

In present investigation, we have prepared a nanocomposites of highly porous MnO2 spongy balls and multi-walled carbon nanotubes (MWCNTs) in thin film form and tested in novel redox-active electrolyte (K3 [Fe(CN)6 ] doped aqueous Na2 SO4 ) for supercapacitor application. Briefly, MWCNTs were deposited on stainless steel substrate by "dip and dry" method followed by electrodeposition of MnO2 spongy balls. Further, the supercapacitive properties of these hybrid thin films were evaluated in hybrid electrolyte ((K3 [Fe(CN)6 doped aqueous Na2 SO4 ). Thus, this is the first proof-of-design where redox-active electrolyte is applied to MWCNTs/MnO2 hybrid thin films. Impressively, the MWCNTs/MnO2 hybrid film showed a significant improvement in electrochemical performance with maximum specific capacitance of 1012 Fg-1 at 2 mA cm-2 current density in redox-active electrolyte, which is 1.5-fold higher than that of conventional electrolyte (Na2 SO4 ). Further, asymmetric capacitor based on MWCNTs/MnO2 hybrid film as positive and Fe2 O3 thin film as negative electrode was fabricated and tested in redox-active electrolytes. Strikingly, MWCNTs/MnO2 //Fe2 O3 asymmetric cell showed an excellent supercapacitive performance with maximum specific capacitance of 226 Fg-1 and specific energy of 54.39 Wh kg-1 at specific power of 667 Wkg-1 . Strikingly, actual practical demonstration shows lightning of 567 red LEDs suggesting "ready-to sell" product for industries.